Messages in this thread Patch in this message | | | Date | Mon, 25 Apr 2022 16:35:37 +0200 | From | Oleg Nesterov <> | Subject | Re: [PATCH v2 2/5] sched,ptrace: Fix ptrace_check_attach() vs PREEMPT_RT |
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On 04/21, Peter Zijlstra wrote: > > +static void clear_traced_quiesce(void) > +{ > + spin_lock_irq(¤t->sighand->siglock); > + WARN_ON_ONCE(!(current->jobctl & JOBCTL_TRACED_QUIESCE));
This WARN_ON_ONCE() doesn't look right, the task can be killed right after ptrace_stop() sets JOBCTL_TRACED | JOBCTL_TRACED_QUIESCE and drops siglock.
> @@ -2290,14 +2303,26 @@ static int ptrace_stop(int exit_code, in > /* > * Don't want to allow preemption here, because > * sys_ptrace() needs this task to be inactive. > - * > - * XXX: implement read_unlock_no_resched(). > */ > preempt_disable(); > read_unlock(&tasklist_lock); > - cgroup_enter_frozen(); > + cgroup_enter_frozen(); // XXX broken on PREEMPT_RT !!! > + > + /* > + * JOBCTL_TRACE_QUIESCE bridges the gap between > + * set_current_state(TASK_TRACED) above and schedule() below. > + * There must not be any blocking (specifically anything that > + * touched ->saved_state on PREEMPT_RT) between here and > + * schedule(). > + * > + * ptrace_check_attach() relies on this with its > + * wait_task_inactive() usage. > + */ > + clear_traced_quiesce();
Well, I think it should be called earlier under tasklist_lock, before preempt_disable() above.
We need tasklist_lock to protect ->parent, debugger can be killed and go away right after read_unlock(&tasklist_lock).
Still trying to convince myself everything is right with JOBCTL_STOPPED/TRACED ...
Oleg.
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